1. Field of the Invention
This invention relates to a method of creating an NC program for pocket machining and, more particularly, to an NC program creation method through which an NC program for pocket machining is created in conversational fashion.
2. Description of the Related Art
Machining (pocket machining) for hollowing out the interior of a profile outline down to a predetermined depth includes such methods as ordinary linear unidirectional cutting, linear zigzag cutting and spiral cutting. In linear unidirectional cutting, the interior of the profile outline is machined by moving a tool in one direction at all times [see FIG. 13(a)]. In linear zigzag cutting, the interior of the profile outline is machined continuously not only in an outward direction but in a return direction as well [see FIG. 13(b)]. In spiral cutting, the interior of the profile outline is machined by moving a tool along offset paths each inwardly offset a predetermined amount from the profile outline [see FIG. 13(c)].
In the prior art, an NC program for such pocket machining is created by automatically deciding the tool path, which is performed upon inputting the profile outline, the pocket machining method (one of the cutting methods of FIGS. 1 through 3), the cutting direction, cut-in direction, finishing allowance, remaining thickness, spindle rotational speed, cutting velocity, tool diameter and the like.
In this conventional method, however, considerable time is required for NC program creation when the profile is a complicated one, and the tool paths includes needless paths (paths which do not contribute to cutting). As a result, cutting efficiency is poor.
FIG. 14 illustrates a tool path 2 for a case in which the interior of a profile 1 is machined by linear zigzag cutting. The portions indicated by the dashed lines do not participate in cutting and represent wasted motion. FIG. 15 illustrates a tool path 3 for a case in which the interior of the profile 1 is machined by spiral cutting. The tool path is complicated, a considerable period of time is required to obtain the tool path, and the cutting time is prolonged.
FIG. 16 illustrates a tool path 4 which is ideal for cutting the interior of the profile 1. The tool path does not contain unneeded path segments and cutting efficiency is high. A method of creating a tool path such as shown in FIG. 16 is not available in the prior art and, as a result, the machining carried out exhibits a poor cutting efficiency.